In hydraulic fracturing, fracturing fluid is injected into a wellbore, penetrating a subterranean formation and forcing the fracturing fluid at pressure to crack and fracture the strata or rock. Proppant is placed in the fracturing fluid and thereby placed within the fracture to form a proppant pack to prevent the fracture from closing when pressure is released, providing improved flow of recoverable fluids, i.e., oil, gas, or water. The success of a hydraulic fracturing treatment is related to the fracture conductivity which is the ability of fluids to flow from the formation through the proppant pack. In other words, the proppant pack or matrix must have a high permeability relative to the formation for fluid to flow with low resistance to the wellbore. Permeability of the proppant matrix may be increased through distribution of proppant and non-proppant materials within the fracture to increase porosity within the fracture.
Prior to injection of the fracturing fluid, the proppant and other components of the fracturing fluid must be blended. Gravity fed proppant addition systems may transfer proppant via gravity free fall to a mixer in order to be added to fracturing fluid. Metering the proppant volume in a gravity fed system may be calculated by determining the flow rate of the proppant through an orifice of a known size when the proppant is in gravity free fall through the orifice. Gravity fed systems may also employ the use of pressurization to aid in transferring proppants into the fluid stream or mixer. Pressurization methods in gravity fed systems may include pressurizing the proppant container subject to the gravity feed or utilizing a venture effect where a smaller diameter pipe is connected to a larger diameter pipe to draw the proppant from the proppant container into the mixer or fluid stream.
Moist, damp proppant is a serious problem that negatively affects the service quality of oilfield well fracturing and gravel packing operations. Existing slurry blending equipment typically relies on the use of proppant that is gravity fed through metering orifices of varying geometry whose openings are adjusted using a mechanical gate. These mechanical metering systems work optimally when proppant is dry and can flow freely. However, moist proppant does not flow in the same manner as dry proppant, and can interfere with the flow of dryer proppant to the point of completely blocking off proppant flow out of the metering gate in some situations, thus affecting the desired proppant concentration in the slurry and negatively affecting service quality of oilfield operations.